Identification of an extracellular bacterial flavoenzyme that can prevent re-polymerisation of lignin fragments

Abstract

Abstract. A significant problem in the oxidative breakdown of lignin is the tendency of phenolic radical fragments to re-polymerise to form higher molecular weight species. In this paper we identify an extracellular flavin-dependent dehydrolipoamide dehydrogenase from Thermobifida fusca that prevents oxidative dimerization of a dimeric lignin model compound, which could be used as an accessory enzyme for lignin depolymerisation.

Characterization of multicopper oxidase CopA from Pseudomonas putida KT2440 and Pseudomonas fluorescens Pf-5: Involvement in bacterial lignin oxidation

“…tomato CopC[38,39].Microbacterium phyllosphaerae contained two copC genes, named as copC886 and copC1032. Gene copC886 (accession number MH924843) was adjacent to a dihydrolipoamide dehydrogenase gene, while copC1032 (accession number MH924844) was situated close to a DyP-type peroxidase gene; both of these gene families have been implicated in lignin degradation[40,41]. The genome of polychlorinated biphenyl degrader Burkholderia xenovorans LB400 contains two copC genes, named as copC-bx1 and copC-bx2, with no other copper resistance genes nearby.…”

Delignification and enhanced gas release from soil containing lignocellulose by treatment with bacterial lignin degraders

“…This behaviour might be due to the tendency of lignin‐oxidizing peroxidases to catalyse repolymerization as well as depolymerization of lignin fragments (Rahmanpour et al . ). For fungal lignin peroxidase, a decrease in phenol content was also observed at low dose, perhaps for the same reason, but at higher dose a dose‐dependent increase in phenol release was observed, with >twofold phenol release at 1 mg g −1 dose.…”

“…Only very small changes were observed upon treatment with P. fluorescens Dyp1B, with a 10% decrease in phenol content at low dose, and 8% increase at high dose, compared with the untreated lignocellulose control. This behaviour might be due to the tendency of lignin-oxidizing peroxidases to catalyse repolymerization as well as depolymerization of lignin fragments (Rahmanpour et al 2017). For fungal lignin peroxidase, a decrease in phenol content was also observed at low dose, perhaps for the same reason, but at higher dose a dose-dependent increase in phenol release was observed, with >twofold phenol release at 1 mg g À1 dose.…”

Enhanced biocatalytic degradation of lignin using combinations of lignin-degrading enzymes and accessory enzymes

“…Dihydrolipoamide dehydrogenase from Thermobifida fusca has been found to act as an accessory enzyme for lignin degradation, by preventing re-polymerisation of phenoxy radicals formed during lignin oxidation. 16 We identified two dihydrolipoamide dehydrogenase enzymes in the genome of lignin-degrading Sphingobacterium sp. T2, which were expressed as His 6 fusion proteins in E. coli and purified (see ESI † Fig.…”

“…In vivo it is thought that this is prevented by oneelectron reduction of phenoxy radicals to phenols via flavindependent accessory enzymes such as cellobiose dehydrogenase in fungi, 15 or dihydrolipoamide dehydrogenase in lignin-degrading bacteria. 16 Therefore, in order to achieve efficient conversion of polymeric lignin into low molecular weight products, it is likely that several ligninoxidising enzymes and accessory enzymes will be needed.…”